This invention relates to the automotive engine revolution speed control device which prevents an abnormal increase in engine revolution when the engine returns from the accelerated condition to the idling condition.
In the conventional automotive gasoline engines, various control functions on the engine, such as an air-fuel ratio control according to the accelerator opening and the load torque, a starting and warm-up adjustment and an idling control, have been done almost solely by the carburetor.
In recent years, however, an electronic engine control system has become widely used, in which various data representing engine running condition is read in using microcomputer so that the engine running condition is controlled comprehensively through various kinds of actuators.
One of the known idling control devices has an actuator to feed-back control the throttle valve opening during idling according to the data from the engine temperature sensor and engine revolution sensor so as to control the engine revolution speed during warm-up (FISC) and the engine revolution speed during idling (ISC).
With this kind of electronic revolution control device, however, the engine revolution is controlled only when the idling detection switch is turned on, so that there is a drawback that when the engine, after being accelerated during warm-up, is returned to the idling condition, the engine revolution will abnormally increases.